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Created page with "'''Fuses and relays''' refers to the electrical protection and control devices used in the Pontiac Fiero. Fuses protect electrical circuits from excessive current. Relays allow a low-current control circuit to switch a higher-current load such as a fan, fuel pump, or other electrical device. == Overview == The Pontiac Fiero uses fuses, fusible links, circuit breakers, and relays throughout the electrical system. These parts are important for diagnosis because man..."
 
 
(33 intermediate revisions by the same user not shown)
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'''Fuses and relays''' refers to the electrical protection and control devices used in the [[Pontiac Fiero]].
'''Fuses and relays''' refers to the fuse block, fuses, circuit breakers, fusible links, and relay-controlled circuits used in the [[Pontiac Fiero]] electrical system.


Fuses protect electrical circuits from excessive current. Relays allow a low-current control circuit to switch a higher-current load such as a fan, fuel pump, or other electrical device.
On the Fiero, many electrical problems can be traced to a blown fuse, poor fuse-block contact, a failed circuit breaker, a bad ground, damaged wiring, or a failed relay in a specific circuit.


== Overview ==
== Fuse access location ==


The Pontiac Fiero uses fuses, fusible links, circuit breakers, and relays throughout the electrical system.
The main fuse block is located under the left side of the instrument panel, on the driver's side.


These parts are important for diagnosis because many electrical problems are caused by blown fuses, poor fuse-panel contacts, failed relays, damaged fusible links, bad grounds, or wiring faults.
Access to the fuses is through a fuse-block access door under the left side of the dash. The access door is released by pushing inward on the two release tabs near the center and swinging the door down toward the seat.


Related topics:
This location makes the fuse block accessible from the driver's footwell area.


* [[Electrical system]]
== Fuse block layout ==
* [[Ground problems]]
* [[Wiring diagrams]]
* [[Connector pinouts]]
* [[No-start diagnosis]]


== Location ==
[[File:fuse_box.png|thumb|right|400px|Fiero fuse block layout.]]


{{Image wanted|Photo showing the Fiero interior fuse panel and common relay locations, preferably with labels or arrows.}}
The Fiero fuse block contains standard blade fuses and circuit breakers.


The main fuse panel is located inside the passenger compartment.
The fuse block includes circuits for engine control, fuel pump, lighting, heater and air conditioning, turn signals, brake lights, power windows, gauges, wipers, radio, courtesy lighting, and power accessories.


Relays are located in several areas depending on circuit and model year. Some relays are located in the front compartment, some in the rear engine compartment, and some near the devices they control.
Because fuse labels are abbreviated, the fuse list below expands the labels into their common circuit meanings.


Because relay locations and circuit details can vary by model year and equipment, the correct wiring diagram should be checked before diagnosis.
<div style="clear: right;"></div>


Related topic:
== Fuse list ==


* [[Wiring diagrams]]
The fuse-block labels most commonly shown for the Fiero are:


== Fuses ==
{| class="wikitable"
! Fuse / breaker label
! Rating
! Common meaning / circuit
! Notes
|-
| ECM IGN
| 10A
| ECM / Computer Command Control ignition feed
| Engine-control ignition power
|-
| F PUMP
| 10A
| Fuel pump relay / oil pressure switch feed
| Fuel pump circuit
|-
| TAIL
| 20A
| Tail lamps, parking lamps, side marker lamps, license plate lamp, and related illumination
| Exterior running lights and related illumination
|-
| FAN E
| 20A
| Coolant fan relay coil; engine/trunk blower on earlier V6 cars where equipped
| Cooling fan control circuit; verify by model year
|-
| TURN B/U
| 20A
| Turn-signal flasher and backup lamps
| Signal / reverse-light related
|-
| TBI INJ1
| 5A
| Throttle-body injection injector circuit 1
| Four-cylinder engine-control related
|-
| STOP HAZ
| 20A
| Stop lamps, hazard flasher, and warning chime
| Brake-light / hazard circuit
|-
| HTR/A/C
| 25A
| Heater / air-conditioning circuit
| HVAC-related power
|-
| GAUGES
| 10A
| Gauges and related warning/control circuits
| Instrument-related circuits
|-
| TBI INJ2
| 5A
| Throttle-body injection injector circuit 2
| Four-cylinder engine-control related
|-
| BAT
| 20A
| Battery-fed circuit
| Constant-power feed for related circuits
|-
| WDO
| 30A circuit breaker
| Power windows
| Power-window protection
|-
| INST LP
| 5A
| Instrument panel lamps and headlight warning
| Dash lighting / warning circuit
|-
| RADIO
| 10A
| Radio and related control circuits
| Radio, cruise control, VSS/TCC-related circuits depending on equipment
|-
| PWR ACC
| 30A circuit breaker
| Power door locks and rear window defogger
| Power accessory circuit
|-
| WIPER
| 25A
| Windshield wiper circuit
| Wiper motor / related circuit
|-
| CTSY/LID
| 25A
| Courtesy lights, rear compartment light, rear lock relay, and power sport mirror control
| Interior courtesy / rear compartment / power mirror-related circuit
|}


A fuse is a protective device designed to open the circuit if current becomes too high.
Because Fieros were offered with different engines, trim levels, and options, the exact downstream loads can vary by year and equipment. The fuse-block labels themselves are usually the most useful starting point for diagnosis.


If a fuse blows, it usually means one of the following:
== Power distribution and fusible links ==


* The circuit was overloaded
The fuse block is only one part of the Fiero power distribution system.
* A wire or component shorted to ground
* The wrong fuse rating was installed
* A component failed internally
* Wiring was damaged
* Previous repairs or modifications caused a fault


A blown fuse should not simply be replaced repeatedly without finding the cause.
The Fiero power distribution system may include:


== Fuse ratings ==
* Fusible links
* Fuses
* Circuit breakers
* Light switch
* Ignition switch
* Related connectors and feed circuits


Fuses are rated by amperage.
Fusible links are short protective wire sections used on higher-current feed circuits. They are intended to melt and stop current flow if excessive current occurs in a part of the electrical system that is not protected by ordinary fuses or circuit breakers.


The replacement fuse should match the correct rating for the circuit. Installing a larger fuse than specified can allow wiring or components to overheat before the fuse opens.
Fusible links should not be replaced with ordinary wire.


A higher-rated fuse should not be used as a “fix” for a fuse that keeps blowing.
Factory service information identifies fusible links in several power-distribution areas, including locations such as the battery junction block, forward lamp harness, starter solenoid, and rear bulkhead connector. Exact fusible-link locations, colors, ratings, and protected circuits should be checked against the correct model-year wiring diagram.


== Fusible links ==
Related topics:


The Fiero also uses fusible links.
* [[Electrical system]]
* [[Wiring diagrams]]
* [[Connector pinouts]]


A fusible link is a short section of special wire designed to act as circuit protection for higher-current circuits. Fusible links are commonly used near main power feeds and charging-system wiring.
== Rear fuse-block connectors ==


A failed fusible link can cause major electrical problems, including loss of power to several circuits.
Some service information shows rear connector cavity locations at the back of the fuse block.


Possible symptoms of a failed fusible link include:
These rear connections can be relevant when diagnosing intermittent power loss, heat damage, loose terminals, or previous wiring repairs.


* No power to multiple circuits
If rear fuse-block connector work is required, use the correct model-year wiring diagram and connector-location information. Do not rely only on the front fuse-block label.
* No-start condition
* Charging-system problems
* Dead electrical system in one area of the car
* Intermittent power loss if the link or connection is damaged


Fusible links should be repaired using the correct type and gauge of fusible-link wire, not ordinary wire.
== Circuit breakers ==


Related topics:
The Fiero fuse block also uses circuit breakers.


* [[Charging system]]
The most obvious circuit breakers shown in the fuse-block diagram are:
* [[No-start diagnosis]]


== Circuit breakers ==
* '''WDO''' – 30A circuit breaker for the power-window circuit
* '''PWR ACC''' – 30A circuit breaker for power-accessory circuits


Some circuits may use circuit breakers instead of ordinary fuses.
The owner's manual also notes that some circuits use circuit-breaker protection instead of an ordinary fuse. Examples include headlight wiring and the windshield wiper motor.


A circuit breaker can open when overloaded and may reset after cooling, depending on type. This can cause an intermittent electrical problem where a circuit works, stops working, and later works again.
Unlike an ordinary fuse, a circuit breaker may open during an overload and later reset. This can create an intermittent problem where a circuit stops working, then works again after the breaker cools.


Circuit breakers are commonly used where temporary overloads can occur, such as motor-driven circuits.
If a circuit breaker repeatedly opens, the cause of the overload should be found rather than bypassing the protection.


== Relays ==
== Flasher and relay locations ==


A relay is an electrically operated switch.
The fuse block protects many circuits, but several flashers and relays are located elsewhere.


Relays allow a low-current circuit to control a higher-current load. This keeps heavy current out of switches and control modules.
The owner's manual identifies these under-dash locations:


A typical relay circuit includes:
* The hazard flasher and horn relay are located under the right side of the instrument panel.
* The turn-signal flasher is located on the left side of the steering column, under the instrument panel.


* Battery or ignition power
The 1988 service manual gives additional component locations, including:
* Ground
* Control signal
* Relay coil
* Relay contacts
* Output to the controlled device


A failed relay can cause a device not to operate even when the fuse is good.
* Fuse block — behind the left side of the instrument panel
* Coolant fan relay — left front corner of the front compartment
* Fuel pump relay — engine compartment, left side of the rear bulkhead
* A/C power relay — front compartment, on the right side of the heater/A/C module
* High-speed blower relay — on the right side of the heater/A/C plenum


== Common Fiero relays ==
These locations are useful starting points, but relay locations and wiring details should still be verified against the correct model-year wiring diagram.


Common relay-controlled systems on the Fiero include:
Related topics:


* [[Fuel pump]]
* [[Fuel pump relay]]
* [[Radiator fan]]
* [[Radiator fan relay]]
* [[Headlights]]
* [[Headlight control module]]
* [[Horn]]
* [[Air conditioning]]
* [[Air conditioning]]
* [[Horn]]
* Rear window defogger, where equipped
* Other electrical accessories depending on model and options


Relay locations and designs should be verified using the correct year wiring information.
== What the common abbreviations mean ==


== Fuel pump relay ==
Some Fiero fuse-block abbreviations are not immediately obvious:


The fuel pump relay controls power to the electric fuel pump.
{| class="wikitable"
! Abbreviation
! Meaning
|-
| ECM IGN
| Engine Control Module ignition feed
|-
| F PUMP
| Fuel pump
|-
| HTR/A/C
| Heater / air conditioning
|-
| TURN B/U
| Turn signals / backup lamps
|-
| TBI INJ1 / INJ2
| Throttle-body injection injector circuits
|-
| STOP HAZ
| Stop lamps / hazards
|-
| WDO
| Power windows
|-
| INST LP
| Instrument lamps
|-
| CTSY/LID
| Courtesy / decklid circuit
|}


A failed fuel pump relay can cause a no-start condition or a delayed-start condition. However, the Fiero fuel pump circuit also has backup behavior through the oil pressure switch on many applications, so diagnosis should not rely on the relay alone.
== Relay-controlled circuits ==


Possible symptoms of fuel pump relay problems include:
The fuse block protects many circuits, but the actual relay for a circuit may be located somewhere else in the car.


* No fuel pump prime
Important relay-controlled circuits include:
* Extended cranking before start
* No-start condition
* Intermittent fuel pump operation
* Fuel pump works only after oil pressure builds
 
Related topics:


* [[Fuel pump]]
* [[Fuel pump]]
* [[Fuel pump relay]]
* [[Radiator fan]]
* [[Fuel pressure test]]
* [[Headlights]]
* [[No-start diagnosis]]
* [[Horn]]
* [[Air conditioning]]


== Radiator fan relay ==
For some circuits, the fuse in the fuse block protects the control or supply side, while the actual load is switched by a relay located elsewhere in the car.


The radiator fan relay controls the radiator fan motor.
Examples:


The relay is part of the higher-current fan motor circuit. It is controlled by the fan switch, air-conditioning system, or related control circuit depending on year and configuration.
* The '''F/PMP''' fuse is part of the fuel-pump circuit, but the actual pump is also controlled by the fuel-pump relay and oil-pressure-switch backup circuit.
 
* The '''HTR/A/C''' circuit is related to HVAC operation, but A/C and radiator-fan operation may also involve relays.
A failed fan relay can cause the radiator fan not to run even if the fan motor itself is good.
* The headlight system differs between 1984-1986 and 1987-1988 Fieros and should be diagnosed using the correct year-specific system information.


Related topics:
Related topics:


* [[Radiator fan]]
* [[Fuel pump relay]]
* [[Radiator fan relay]]
* [[Radiator fan relay]]
* [[Radiator fan switch]]
* [[Headlight control module]]
* [[Overheating]]
 
== Headlight relays and modules ==
 
The Fiero headlight system differs between early and late model years.
 
1984-1986 Fieros use the first-generation headlight motor system.
 
1987-1988 Fieros use the second-generation headlight system with a different control design.
 
Because the systems are different, relay and control diagnosis should be matched to the correct model year.
 
Related topics:
 
* [[Headlights]]
* [[Headlight motor problems]]
* [[Headlight motor problems]]
* [[Headlight control module]]


== Horn relay ==
== Common fuse-block problems ==


The horn circuit uses a relay so the horn switch does not carry the full horn current.
Common Fiero fuse and fuse-block problems include:


A horn problem may be caused by the fuse, relay, horn switch, horn itself, wiring, or ground.
* Blown fuse
* Fuse installed with the wrong amperage
* Poor contact between fuse and fuse-block terminals
* Corrosion
* Heat damage
* Previous-owner wiring modifications
* Loose rear connector cavities
* Circuit breaker failure
* Repeatedly blown fuse caused by a short or failed component


Possible symptoms include:
A blown fuse should not simply be replaced repeatedly without finding the cause.


* Horn does not work
== Diagnosis ==
* Horn works intermittently
* Horn sounds weak
* Horn stays on
* Clicking relay but no horn sound


Related topic:
When diagnosing a Fiero fuse or relay-related electrical problem:


* [[Horn]]
# Identify the affected circuit.
 
# Check the correct fuse or circuit breaker.
== Relay testing ==
# Verify the fuse rating.
 
# Check for power on both sides of the fuse.
Relay diagnosis usually involves checking both the control side and the load side of the circuit.
# Inspect the fuse-block terminals for corrosion or looseness.
# Check the rear connector cavities if there is evidence of heat or intermittent power loss.
# If the circuit also uses a relay, test that relay and the related wiring.
# Inspect grounds.
# Inspect for aftermarket wiring or previous repairs.


Basic checks include:
A fuse that looks good visually may still have poor contact or may not be receiving power.
 
# Check the related fuse.
# Identify the correct relay.
# Check for power at the relay.
# Check for ground where required.
# Check whether the relay receives a control signal.
# Listen or feel for relay clicking.
# Check whether power leaves the relay when activated.
# Test or swap with a known-good relay only when the relay type and circuit are correct.
# Check the controlled device separately.
# Check wiring and grounds.
 
A relay that clicks is not always good. The internal contacts may still be burned, weak, or unable to carry current.
 
== Fuse testing ==
 
A fuse can sometimes look good visually but still be faulty or have poor contact.
 
Useful checks include:
 
* Visual inspection
* Test light check on both sides of the fuse
* Multimeter continuity check
* Voltage check under load
* Fuse-panel contact inspection
* Checking for corrosion or heat damage
 
The most useful in-car test is often to check for power on both sides of the fuse while the circuit should be powered.


== Repeatedly blown fuses ==
== Repeatedly blown fuses ==


A fuse that blows repeatedly indicates a fault.
A fuse that blows repeatedly indicates a fault somewhere in the circuit.


Possible causes include:
Possible causes include:


* Short to ground
* Short to ground
* Damaged wiring
* Pinched or chafed wiring
* Failed motor
* Failed motor
* Failed relay or switch
* Failed relay
* Failed switch
* Incorrect bulb or component
* Incorrect bulb or component
* Incorrect fuse rating
* Aftermarket wiring fault
* Water intrusion
* Water intrusion
* Chafed wire
* Poor aftermarket wiring
* Pinched wire after repair work
 
Do not install a larger fuse to stop a fuse from blowing. The correct repair is to find and fix the cause of the excessive current.
 
== Intermittent electrical problems ==
 
Fuse and relay problems can be intermittent.
 
Possible causes include:
 
* Loose fuse-panel contacts
* Corrosion
* Heat-related relay failure
* Vibration-sensitive connection
* Loose relay socket
* Damaged wiring
* Weak ground
* Poor previous repair
* Fuse that loses contact in the panel
 
Intermittent problems should be diagnosed by checking power and ground while the fault is present, when possible.
 
Related topic:
 
* [[Ground problems]]
 
== Aftermarket wiring ==
 
Many Fieros have had aftermarket radios, alarms, amplifiers, lighting, gauges, engine swaps, or other electrical accessories installed.
 
Aftermarket wiring can cause fuse and relay problems if it is poorly installed.
 
Common problems include:
 
* Incorrect power source
* No fuse protection
* Oversized fuse
* Poor ground
* Scotch-lock or crimp connector failure
* Wires routed near sharp edges
* Wires routed near heat
* Added load on an existing circuit
* Removed or bypassed factory protection
 
Aftermarket circuits should be inspected when diagnosing unexplained fuse failures or electrical problems.
 
== Diagnosis ==
 
Basic fuse and relay diagnosis includes:
 
# Identify the affected circuit.
# Check the correct fuse.
# Verify the fuse rating.
# Check for power on both sides of the fuse.
# Check the related relay, if equipped.
# Check for relay control power and ground.
# Check relay output.
# Check the controlled device.
# Check wiring between the fuse, relay, switch, and load.
# Check grounds.
# Inspect for previous repairs or modifications.
# Use the correct wiring diagram for the model year.
 
Diagnosis should be circuit-specific. Guessing and replacing parts can miss wiring faults, poor grounds, or incorrect previous repairs.
 
== Common mistakes ==
 
Common mistakes during fuse and relay diagnosis include:
 
* Replacing a blown fuse without finding the cause
* Installing a higher-rated fuse
* Assuming a relay is good because it clicks
* Testing only the fuse and not the circuit
* Ignoring grounds
* Ignoring fusible links
* Assuming all model years are wired the same
* Swapping relays without confirming pin layout
* Overlooking aftermarket wiring
* Overlooking corrosion or loose terminals
 
== Service notes ==
 
When working on fuses and relays:


* Use the correct fuse rating.
Do not solve a repeatedly blown fuse by installing a higher-rated fuse.
* Do not bypass fuses.
* Do not replace fusible links with ordinary wire.
* Disconnect the battery when working on major wiring repairs.
* Use wiring diagrams for the correct model year.
* Check grounds as well as power feeds.
* Inspect relay sockets and fuse-panel contacts.
* Label added wiring when possible.
* Repair damaged wiring properly.
* Protect wiring from heat, sharp edges, and moving parts.


== Notes ==
== Notes ==


Fuses and relays are simple parts, but they are part of larger circuits.
This page is mainly a Fiero fuse-block overview.


A blown fuse, failed relay, or bad fusible link is often a symptom of another problem. Good diagnosis should look at the fuse or relay, the wiring, the load, the switch or control circuit, and the ground path.
For detailed circuit diagnosis, it is often better to continue to the specific circuit page, such as:


== Forum discussions ==
* [[Fuel pump]]
 
* [[Radiator fan]]
Useful repair or diagnostic threads may be added here when they contain practical fuse, relay, or electrical troubleshooting information.
* [[Headlights]]
* [[Horn]]
* [[Air conditioning]]
* [[Electrical system]]


== See also ==
== See also ==
Line 346: Line 327:
* [[Wiring diagrams]]
* [[Wiring diagrams]]
* [[Connector pinouts]]
* [[Connector pinouts]]
* [[No-start diagnosis]]
* [[Fuel pump]]
* [[Fuel pump]]
* [[Fuel pump relay]]
* [[Fuel pump relay]]
* [[Radiator fan]]
* [[Radiator fan]]
* [[Radiator fan relay]]
* [[Radiator fan relay]]
* [[Radiator fan switch]]
* [[Headlights]]
* [[Headlights]]
* [[Headlight motor problems]]
* [[Headlight motor problems]]
* [[Headlight control module]]
* [[Headlight control module]]
* [[Charging system]]
* [[Horn]]
* [[Horn]]
* [[Overheating]]
* [[Air conditioning]]
* [[No-start diagnosis]]
* [[Fuse block]]
* [[Circuit breakers]]
* [[Hazard flasher]]
* [[Turn signal flasher]]
* [[Power distribution]]
* [[Fusible links]]


[[Category:Fieropedia]]
[[Category:Fieropedia]]
[[Category:Electrical system]]
[[Category:Electrical system]]
[[Category:Diagnostics]]
[[Category:Service procedures]]
[[Category:Service procedures]]
[[Category:Diagnostics]]
[[Category:Reference]]
[[Category:Reference]]

Latest revision as of 00:16, 19 July 2026

Fuses and relays refers to the fuse block, fuses, circuit breakers, fusible links, and relay-controlled circuits used in the Pontiac Fiero electrical system.

On the Fiero, many electrical problems can be traced to a blown fuse, poor fuse-block contact, a failed circuit breaker, a bad ground, damaged wiring, or a failed relay in a specific circuit.

Fuse access location

The main fuse block is located under the left side of the instrument panel, on the driver's side.

Access to the fuses is through a fuse-block access door under the left side of the dash. The access door is released by pushing inward on the two release tabs near the center and swinging the door down toward the seat.

This location makes the fuse block accessible from the driver's footwell area.

Fuse block layout

Fiero fuse block layout.

The Fiero fuse block contains standard blade fuses and circuit breakers.

The fuse block includes circuits for engine control, fuel pump, lighting, heater and air conditioning, turn signals, brake lights, power windows, gauges, wipers, radio, courtesy lighting, and power accessories.

Because fuse labels are abbreviated, the fuse list below expands the labels into their common circuit meanings.

Fuse list

The fuse-block labels most commonly shown for the Fiero are:

Fuse / breaker label Rating Common meaning / circuit Notes
ECM IGN 10A ECM / Computer Command Control ignition feed Engine-control ignition power
F PUMP 10A Fuel pump relay / oil pressure switch feed Fuel pump circuit
TAIL 20A Tail lamps, parking lamps, side marker lamps, license plate lamp, and related illumination Exterior running lights and related illumination
FAN E 20A Coolant fan relay coil; engine/trunk blower on earlier V6 cars where equipped Cooling fan control circuit; verify by model year
TURN B/U 20A Turn-signal flasher and backup lamps Signal / reverse-light related
TBI INJ1 5A Throttle-body injection injector circuit 1 Four-cylinder engine-control related
STOP HAZ 20A Stop lamps, hazard flasher, and warning chime Brake-light / hazard circuit
HTR/A/C 25A Heater / air-conditioning circuit HVAC-related power
GAUGES 10A Gauges and related warning/control circuits Instrument-related circuits
TBI INJ2 5A Throttle-body injection injector circuit 2 Four-cylinder engine-control related
BAT 20A Battery-fed circuit Constant-power feed for related circuits
WDO 30A circuit breaker Power windows Power-window protection
INST LP 5A Instrument panel lamps and headlight warning Dash lighting / warning circuit
RADIO 10A Radio and related control circuits Radio, cruise control, VSS/TCC-related circuits depending on equipment
PWR ACC 30A circuit breaker Power door locks and rear window defogger Power accessory circuit
WIPER 25A Windshield wiper circuit Wiper motor / related circuit
CTSY/LID 25A Courtesy lights, rear compartment light, rear lock relay, and power sport mirror control Interior courtesy / rear compartment / power mirror-related circuit

Because Fieros were offered with different engines, trim levels, and options, the exact downstream loads can vary by year and equipment. The fuse-block labels themselves are usually the most useful starting point for diagnosis.

The fuse block is only one part of the Fiero power distribution system.

The Fiero power distribution system may include:

  • Fusible links
  • Fuses
  • Circuit breakers
  • Light switch
  • Ignition switch
  • Related connectors and feed circuits

Fusible links are short protective wire sections used on higher-current feed circuits. They are intended to melt and stop current flow if excessive current occurs in a part of the electrical system that is not protected by ordinary fuses or circuit breakers.

Fusible links should not be replaced with ordinary wire.

Factory service information identifies fusible links in several power-distribution areas, including locations such as the battery junction block, forward lamp harness, starter solenoid, and rear bulkhead connector. Exact fusible-link locations, colors, ratings, and protected circuits should be checked against the correct model-year wiring diagram.

Related topics:

Rear fuse-block connectors

Some service information shows rear connector cavity locations at the back of the fuse block.

These rear connections can be relevant when diagnosing intermittent power loss, heat damage, loose terminals, or previous wiring repairs.

If rear fuse-block connector work is required, use the correct model-year wiring diagram and connector-location information. Do not rely only on the front fuse-block label.

Circuit breakers

The Fiero fuse block also uses circuit breakers.

The most obvious circuit breakers shown in the fuse-block diagram are:

  • WDO – 30A circuit breaker for the power-window circuit
  • PWR ACC – 30A circuit breaker for power-accessory circuits

The owner's manual also notes that some circuits use circuit-breaker protection instead of an ordinary fuse. Examples include headlight wiring and the windshield wiper motor.

Unlike an ordinary fuse, a circuit breaker may open during an overload and later reset. This can create an intermittent problem where a circuit stops working, then works again after the breaker cools.

If a circuit breaker repeatedly opens, the cause of the overload should be found rather than bypassing the protection.

Flasher and relay locations

The fuse block protects many circuits, but several flashers and relays are located elsewhere.

The owner's manual identifies these under-dash locations:

  • The hazard flasher and horn relay are located under the right side of the instrument panel.
  • The turn-signal flasher is located on the left side of the steering column, under the instrument panel.

The 1988 service manual gives additional component locations, including:

  • Fuse block — behind the left side of the instrument panel
  • Coolant fan relay — left front corner of the front compartment
  • Fuel pump relay — engine compartment, left side of the rear bulkhead
  • A/C power relay — front compartment, on the right side of the heater/A/C module
  • High-speed blower relay — on the right side of the heater/A/C plenum

These locations are useful starting points, but relay locations and wiring details should still be verified against the correct model-year wiring diagram.

Related topics:

What the common abbreviations mean

Some Fiero fuse-block abbreviations are not immediately obvious:

Abbreviation Meaning
ECM IGN Engine Control Module ignition feed
F PUMP Fuel pump
HTR/A/C Heater / air conditioning
TURN B/U Turn signals / backup lamps
TBI INJ1 / INJ2 Throttle-body injection injector circuits
STOP HAZ Stop lamps / hazards
WDO Power windows
INST LP Instrument lamps
CTSY/LID Courtesy / decklid circuit

Relay-controlled circuits

The fuse block protects many circuits, but the actual relay for a circuit may be located somewhere else in the car.

Important relay-controlled circuits include:

For some circuits, the fuse in the fuse block protects the control or supply side, while the actual load is switched by a relay located elsewhere in the car.

Examples:

  • The F/PMP fuse is part of the fuel-pump circuit, but the actual pump is also controlled by the fuel-pump relay and oil-pressure-switch backup circuit.
  • The HTR/A/C circuit is related to HVAC operation, but A/C and radiator-fan operation may also involve relays.
  • The headlight system differs between 1984-1986 and 1987-1988 Fieros and should be diagnosed using the correct year-specific system information.

Related topics:

Common fuse-block problems

Common Fiero fuse and fuse-block problems include:

  • Blown fuse
  • Fuse installed with the wrong amperage
  • Poor contact between fuse and fuse-block terminals
  • Corrosion
  • Heat damage
  • Previous-owner wiring modifications
  • Loose rear connector cavities
  • Circuit breaker failure
  • Repeatedly blown fuse caused by a short or failed component

A blown fuse should not simply be replaced repeatedly without finding the cause.

Diagnosis

When diagnosing a Fiero fuse or relay-related electrical problem:

  1. Identify the affected circuit.
  2. Check the correct fuse or circuit breaker.
  3. Verify the fuse rating.
  4. Check for power on both sides of the fuse.
  5. Inspect the fuse-block terminals for corrosion or looseness.
  6. Check the rear connector cavities if there is evidence of heat or intermittent power loss.
  7. If the circuit also uses a relay, test that relay and the related wiring.
  8. Inspect grounds.
  9. Inspect for aftermarket wiring or previous repairs.

A fuse that looks good visually may still have poor contact or may not be receiving power.

Repeatedly blown fuses

A fuse that blows repeatedly indicates a fault somewhere in the circuit.

Possible causes include:

  • Short to ground
  • Pinched or chafed wiring
  • Failed motor
  • Failed relay
  • Failed switch
  • Incorrect bulb or component
  • Water intrusion
  • Poor aftermarket wiring

Do not solve a repeatedly blown fuse by installing a higher-rated fuse.

Notes

This page is mainly a Fiero fuse-block overview.

For detailed circuit diagnosis, it is often better to continue to the specific circuit page, such as:

See also

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